For a little more than alum you can get a Stiletto($250ish shipped) from my friend. I would use the stiletto and keep the SSt as a spare. SSt are good props but basically a stronger alternative to alum. A good Stiletto or ?? should help performance. If you are happy with a 21 SSt I think a Stiletto 20 would be good as they are more aggressive than a SST. If interested in his contact info....e-mail me as I rarely check PM's. He would be able to give you good advice as well, a real prop guru as all props are designed differently. The Stiletto might give more bow lift where a the Viper gave too much stern, etc.
Nick
1994 22' Classic-454 B1 Red & white
1981 13' Whaler sport(original owner)
South Tampa Bay, FL "May I mamoo dogface to the banana patch?"